A. Field of Invention
This invention pertains to a display apparatus which receives digital signals and converts the same into moving images. More particularly, the subject invention pertains to an apparatus and method in which asymmetrical stroboscopy is used to eliminate spatial and temporal artefacts from the moving images.
B. Description of the Prior Art
Historically, motion pictures have been recorded as a series of still positive transparent images or frames on a transparent media (e.g., film). The images were then projected as a sequence of frames at a relatively fast rate (normally at 24 frames per second) on a passive screen. These still images are perceived by the human eye as moving pictures. Three separate physiological phenomenon contribute to this effect: persistence of vision, phenomenal movement (also known as the Phi effect) and a specific stroboscopic phenomenon which is referred to herein as the xe2x80x98blink effectxe2x80x99. The first phenomenon refers to the eye""s ability to retain an image for a period of time after it impinges on the retina. The second phenomenon pertains to the eye""s propensity to interpret similar images projected in quick sequence on the retina as corresponding to a moving object. The third phenomenon is very important in dealing with images of moving objects. This phenomenon is based on the eye""s perception of similar images interrupted by a black interval. The eye (or more properly, the visual cortex of the brain) interprets the black interval as an eye blink and two similar images separated by the black period are interpreted as representing a moving object. Advantageously, as a film is shown via a standard movie projector, its frames are separated by a black interval generated by a shutter while a current frame is replaced by a succeeding frame. The duration of this black interval is commensurate with the blink effect.
A problem with standard motion picture projectors is that they are only capable of showing moving images from a transparent film. Another problem with these projectors is that they cannot be used to show moving images from digital signals and therefore the digital signals must be converted into images that are then recorded on a standard film. This process is expensive, and the various conversion steps degrade the picture quality.
During the last several years, digital projectors have been developed which can be used to project moving images from digital signals. As many content providers are adapting digital technology as a means of creating motion pictures, digital projectors are gaining acceptance as the primary means for generating motion pictures. However, independently of what technology they use, digital projectors do not utilize shutters. Therefore, the images that make up a typical motion picture are not separated by black intervals and the blink effect is not present. As a result, when a motion picture is shown through a digital projector, its images appear jerky or smeared. Surprisingly, this effect can occur at both very high and very low rates, as explained in more detail below.
In view of the above-disadvantages of the prior art, it is an objective of the present invention to provide a digital projector that has an improved motion rendition by inducing a blink effect in the viewer""s eyes.
A further objective is to provide a digital projector with an improved performance without requiring major changes in its design.
Other objectives and advantages of the invention shall become apparent from the following description of the invention. Briefly, the subject application pertains to a digital projector having an input receiving digital data defining image frames; and an optical modulator adapted to generate a sequence of images of a moving object corresponding to the digital data. Advantageously, the images are generated in such a manner that they are separated by black intervals selected to induce a blink in the eye of a viewer. The duration and occurrence of these black intervals are defined by blink signals. By using these blink signals the projector, broadly speaking, mimics or imitates the operation of the shutter on a standard movie projector. In this manner the quality and smoothness of the images being projected is visibly improved. Preferably the black intervals are synchronized so that at least one black interval occurs during each frame. The black intervals have a duration in the range of 1-20 msec.
In another aspect of the invention, a digital projector adapted to generate moving images from a stream of data consisting of digital frames is disclosed having an input adapted to receive the stream of data and a timer adapted to generate blink signals in synchronism with the digital frames. An optical image generator is used to generate a sequence of optical images corresponding to the sequence of digital frames, the optical images being separated by or interspaced by black intervals defined by the blink signals, the black intervals being spaced to induce a blink effect in the eyes of the viewers.
The optical image generator preferably includes a light source generating light and an optical modulator receiving the light and modulating it in accordance with digital frames. The projector further includes a mixer adapted to generate control signals for the optical modulator in accordance with the digital frames and the blink signals. The mixer is adapted to generate modified frames, each frame including a black interval and data from one of the digital frames.
In another aspect of the invention a method of generating moving images from data is disclosed by generating blink signals selected to induce a blink effect in the eyes of a viewer; converting the data into images; and projecting said images and the blink signals in sequence with images being interspaced by blink signals. Preferably no light is projected during said black intervals.